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Quadraphonics - Quad - The Rivals

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QUAD - THE RIVALS


STEREO QUADRAPHONIC

SQ emerged from the CBS Technology Center in April 1971. Rear channel information was cut into the record using an intricate process which added double helical groove modulations, alongside vectored modulations for the front channels. By sensing the phase relationships between the channels, the SQ decoder attempted to send the appropriate signals to the appropriate loudspeaker. This idea of a ‘non-symmetrical phase matrix’ using phase shift networks to divide up the sounds was a very sophisticated one for 1971. The results weren’t spectacular, giving only around 3dB of channel separation between the front and rear speakers – due to the need to retain excellent left-to-right separation at the front. Later ‘logic decoders’ gave far better results. Any matrix quad system (SQ, QS/RM, EV-4) decoded any matrix-encoded record, but the results weren’t always consistent!


QUADRAPHONIC STEREO

Sansui introduced QS in February 1972. Like SQ and EV-4, it could decode any matrixed quad encoded record, and synthesise quad from a stereo source. A very close cousin was RM (Regular Matrix), which is said to be QS but without logic in the decoder. QS was often said to be dramatically better than SQ when synthesising quad from a stereo source, giving up to 20dB front to rear separation and 10dB from left to right. By 1973, Sansui had developed its SQ decoders with logic circuitry and a range of parameter adjustments to give ‘Vario-Matrix’. The quad cognoscenti generally agree this works very well, making stereo and matrixed quad discs sound vibrant and engaging.

COMPATIBLE DISCRETE-4 CHANNEL

A discrete four channel surround sound from vinyl, CD-4 pushed record manufacturing technology to the limit! A high frequency carrier signal (a la FM stereo) handled two extra channels of audio in RCA’s CD-4 Quadradisc system launched in May 1972. Super-fine grooves were cut into the vinyl to carry signals between 20-45kHz, which the CD-4 demodulator sensed and ‘downconverted’ to the audio band of around 100Hz-15,000kHz and sent to rear loudspeakers.

The limitations of tonearms of the day created difficulties. Shibata styli needed tracking at less than 2g – routine today but fanciful back then. Mistreatment, dirt and worn styli simply wiped out the HF information. Finally, CD-4’s channel separation wasn’t obviously better than later matrix decoders, which were far easier to use.



 
Comments (3)
"Decent two channel stereo"...
3Saturday, 04 April 2015 16:31
AAL
"At a time when technology barely enabled decent two-channel stereo" In the 1970s?!?

You have to be kidding. We are not talking about the 1930s! Who writes such things, I wonder, and how old is he or she...

The LP managed two channels at a push; trying to squeeze in four was beyond elegantly achievable.
Decoding matrix quad via Dolby Pro Logic II
2Friday, 23 November 2012 15:21
Jay
The Dolby Pro Logic II decoder does a very fine job decoding QS-matrixed recordings, with spot-on rear speaker placement of sounds. SQ recordings also deliver a good quad effect, but rear channel placements of sounds will not be completely accurate. The effect is still pleasing, but not as discrete as QS. The logic steering circuitry, used in PL II, are similar to the Tate-DES circuits used in some later SQ decoders, but geared mainly for the Dolby MP matrix. This matrix is similar enough to QS to yield excellent results.

Thanks Jay. This is one obscure subject. For the benefit of those scratching their heads, we are talking about decoding Four Channel SQ and QS LPs from the 1970s. You either have them in your LP collection because you were there at the time (me!) or you get them at car boot sales, charity shops etc, or from eBay. Buy an AV receiver with a phono input (or use an external phono stage) and you can then decode these discs through Dolby Pro Logic II for four-channel surround-sound. Oh what fun!
Decode quadradisc vinyls now
1Tuesday, 13 December 2011 13:42
Juan Carlos
Is it possible to decode the signal from a quadradisc vinyl with a home theater decoder?

It is possible to decode CBS SQ and Sansui QS, both matrix encoded discs, but not JVC CD-4. You will find this interesting, even if the results are a little approximate. Also, try putting TV sound through the receiver with matrix decoding switched on. You will find sounds coming out of the rear loudspeakers - entertaining!

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